1. Field of the Invention
The present invention relates in general to a watercraft, and more specifically to a vertically adjustable outboard drive of a watercraft.
2. Description of Related Art
The desirable trim angle of an outboard drive varies with watercraft running condition. For instance, the bow of the watercraft should press against the water when accelerating from rest or from a slow speed. To achieve this condition, the angle of the propeller shaft is disposed at a negative angle relative to the horizontal (i.e., at a negative trim angle). That is, a thrust vector produced by the propeller is out of the water. When running at high speed, the propeller is raised or trimmed to position the propeller shaft at a positive trim angle relative to the horizontal within the range of about 0.degree. to 15.degree..
The desirable height or vertical location of the propeller of the outboard drive in the water in which the watercraft is operated also varies depending upon the running condition of the watercraft. When accelerating from low speeds, the vertical position of the outboard drive should remain relatively low in the water until the watercraft reaches a planing condition. Up until that time, the vertical position should not change, but trim condition is adjusted to obtain optimum acceleration and subsequently to maintain cruising speed once on plane. The propeller of the outboard drive is raised once the watercraft is on plane so as to minimize water resistance of the lower unit (i.e., reduce drag on the lower unit) and to improve stability.
Various linkage and suspension systems have been proposed in connection with outboard motors to allow for adjustment of the tilt and lift positions of the outboard motor to gain the advantages of the above principles. Prior stern drives, however, have not provided for both tilt and lift adjustment of the drive.